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Spark Plug replacement

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Updated 10 Oct 2019

Joel Ilton

How much do Spark Plugs cost?

Depending on how many cylinders your vehicle has, whether it requires normal or precious metal spark plugs and the location of the spark plugs, the price to have them replaced can vary quite significantly.

On a normal 4-cylinder engine with standard spark plugs, replacement cost can start around $120 up to $150+, or if precious metal spark plugs are required, $150 up to $200+.

6 cylinder and 8 Cylinder engines will increase in price, as more spark plugs are required.

Replacing spark plugs in these vehicles usually starts around the $200 mark and can go up to $300+ depending on inlet manifold removal and installation.

What do the Spark Plugs do?

The spark plugs are one of the most important components in a petrol internal combustion engine.

Their main job is to ignite the air and fuel mixture inside the cylinders.

The ignition system supplies voltage to the spark plug at specific intervals controlled by the Engine Control Unit or an Ignition module.

They do wear out over time and most manufacturers have specific kilometre and time intervals for replacement.

If they are not replaced, the air fuel mixture will be harder to ignite, causing the engine to misfire and increase fuel consumption.

Most engines will have a spark plug for each cylinder, although some manufacturers will use two spark plugs per cylinder.

On some vehicles, removal of the intake manifold is required to get to the spark plugs.

How are the Spark Plugs replaced?

  • The vehicles computer system is scanned for any Diagnostic Trouble Codes (DTC)
  • The bonnet is opened and the surface around the ignition system is cleaned of dirt and debris
  • The inlet manifold is removed (If required)
  • The ignition leads or coil packs are disconnected, and the spark plugs removed
  • The threads in the cylinder head are inspected for damage
  • The old spark plugs are inspected for any signs of damage
  • If requested, a compression test may be carried out (at an additional charge)
  • The new spark plug gaps are measured and then fitted into the cylinder head
  • The ignition leads or coil packs are refitted and the inlet manifold is refitted with new gaskets (If removed)
  • The engine is started to ensure correct operation and any DTC’s are cleared from the computer system.

Common signs your Spark Plugs may require replacing:

  • Decreasing fuel economy
  • Increased engine vibration or engine misfire
  • Poor engine performance
  • Check Engine Light is on

How important is replacing worn Spark Plugs?

Operating a vehicle that has excessively worn spark plugs can cause other damage, especially if the vehicle is misfiring.

This allows unburned fuel to enter the exhaust and may cause expensive damage to the catalytic converter, as well as expensive internal engine damage.

If you notice any of these symptoms, have your vehicle inspected by one of AutoGuru's 1,600+ qualified workshops, or have a fully certified mobile mechanic come to your house or office – Too Easy!

Image credit: For Want of a Nail- HJL, Sparks? - Stuart.H

All data gathered in December 2016. 

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Written By

Joel Ilton

Finding a passion for cars from a young age, Joel carried out work experience as a mechanic whilst at school before starting an apprenticeship after finishing year 12.

After almost 10 years on the tools and in customer service, he moved into the IT realm as a Data Analyst and In-House mechanic at AutoGuru.